def find_previous_power_of_two(number: int) -> int: """ Find the largest power of two that is less than or equal to a given integer. https://stackoverflow.com/questions/1322510 >>> [find_previous_power_of_two(i) for i in range(18)] [0, 1, 2, 2, 4, 4, 4, 4, 8, 8, 8, 8, 8, 8, 8, 8, 16, 16] >>> find_previous_power_of_two(-5) Traceback (most recent call last): ... ValueError: Input must be a non-negative integer >>> find_previous_power_of_two(10.5) Traceback (most recent call last): ... ValueError: Input must be a non-negative integer """ if not isinstance(number, int) or number < 0: raise ValueError("Input must be a non-negative integer") if number == 0: return 0 power = 1 while power <= number: power <<= 1 # Equivalent to multiplying by 2 return power >> 1 if number > 1 else 1 if __name__ == "__main__": import doctest doctest.testmod()